Insane Dancing...

And those seen dancing were thought insane by those who could not hear the music. Though I wonder if Nietzsche would have said that in the age of ear buds.

There is a certain "sharpness" to the motions of a professional dancer that I see in abundance in that video. I notice it too in Glee when Heather Morris (Brittany), who is the one primarily professional dancer (even if it was for Beyonce), is dancing with the others -- I can always pick her out in the group of also very good and well coached dancers from how sharp and exactly she executes the moves.